1. Field of the Invention
The present invention relates to a dielectric duplexer mainly used in the microwave band, and a communication apparatus using the same.
2. Description of the Related Art
A typical dielectric duplexer is described with reference to FIG. 11.
FIG. 11 is a perspective view of the appearance of a typical dielectric duplexer.
Referring to FIG. 11, a substantially rectangular dielectric block 1 includes inner-conductor-containing holes 2a to 2f having inner conductors 3a to 3f formed on the inner surfaces thereof, respectively, and an outer conductor 5 formed on the entire outer surface thereof. Inner-conductor-unformed portions 4a to 4f on which the inner conductors 3a to 3f are not formed are formed in the vicinity of first ends of the inner-conductor-containing holes 2a to 2f, and the first ends are open. Second ends that are opposite to the first ends are short circuited. Thus, dielectric resonators are constructed. Each of the inner-conductor-containing holes 2a to 2f is stepped so that the open end side has a larger inner diameter than the short circuited end side.
On the outer surface of the dielectric block 1, input/output electrodes 6 and 7, which are separated from the outer conductor 5, are formed so as to extend from the end surfaces in the alignment direction of the inner-conductor-containing holes 2a to 2f to the mounting surface that faces the mounting substrate. On the outer surface of the dielectric block 1, an input/output electrode 8, which is separated from the outer conductor 5, is further formed between the inner-conductor-containing holes 2c and 2d so as to extend from the open end surface of the inner-conductor-containing holes 2a to 2f to the mounting surface. With this structure, a first group of the inner-conductor-containing holes 2a to 2c, and a second group of the inner-conductor-containing holes 2d to 2f each form a three-stage dielectric filter having a coupling capacitor, thereby forming a dielectric duplexer as a whole.
Specifically, the dielectric block 1, the inner conductors 2a to 2f, and the outer conductor 5 constitute TEM (transverse electromagnetic) mode resonators, and the TEM mode resonators are combline-coupled with each other by means of stray capacitance generated in the inner-conductor-unformed portions 4a to 4f to form dielectric filters. The plurality of dielectric filters are combined to form a dielectric duplexer. The dielectric duplexer has attenuation poles (coupling poles) because of coupling between the resonators. The attenuation poles can be used to provide a sharp attenuation characteristic from the pass band to the cut-off band near a low frequency region or from the pass band to the cut-off band near a high frequency region.
However, such a typical dielectric duplexer has encountered a problem to be overcome.
In a dielectric duplexer having a substantially rectangular dielectric block and an outer conductor formed on the outer surface thereof, a resonance mode other than a basic resonance mode or a TEM mode, including a TE101 mode, may be generated by the dielectric block and the outer conductor. Once a resonance mode different from a basic resonance mode, such as a TE mode, is generated, the dielectric duplexer will increase spurious responses.
In order to overcome such a problem, approaches which have been contemplated are (1) to modify the dimensions of a dielectric duplexer to offset the resonant frequency of a TE mode, and (2) to separately provide a transmission filter and a reception filter which are combined so that the influence of a TE mode on the dielectric duplexer may be reduced.
In approach (1), the dimensions of the dielectric duplexer must be defined with consideration of a TE mode, and a filter design accommodating a TEM mode is required. Furthermore, since a compact dielectric duplexer is desirable in the current state, there are limitations to variable dimensions, leading to less flexibility in design.
In approach (2), since two components are required for a transmission filter and a reception filter, the number of circuit components increases, resulting in increased production cost. The transmission filter and the reception filter are bonded by soldering, thereby reducing reliability.
Accordingly, it is an object of the present invention to provide a dielectric duplexer which eliminates or reduces the influence of a TE mode and has low spurious responses without the need to modify the dimensions or connect additional components, and to provide a communication apparatus using the dielectric duplexer.
To this end, in one aspect of the present invention, a dielectric duplexer includes:
a dielectric block;
a plurality of inner-conductor-containing holes formed in the dielectric block, each hole having an inner conductor formed on the inner surface thereof, the inner-conductor-containing holes extending from one surface to another surface opposite thereto of the dielectric block;
an outer conductor and an input/output terminal which are formed on the outer surface of the dielectric block, the input/output terminal being separated from the outer conductor; and
at least one short circuited conductor formed between the plurality of inner-conductor-containing holes on a transmitter side and the plurality of inner-conductor-containing holes on a receiver side, said at least one short circuited conductor extending from one surface that is parallel to the axes of the inner-conductor-containing holes to another surface opposite thereto and conductively coupled to said outer conductor.
Therefore, the dielectric duplexer is affected less by a TE mode and has low spurious responses.
The dielectric block may include an excitation hole for an antenna, and the at least one short circuited conductor preferably intersects the excitation hole. Therefore, the dielectric duplexer has low spurious responses.
In another aspect of the present invention, a communication apparatus incorporates the dielectric duplexer, thereby achieving the desired communication characteristics.